The invention relates to a tensioning device for traction means, such as belts or chains, with a housing-like part, in which a tensioning mechanism and a spring element biasing the tensioning mechanism for tightening the traction means are mounted, whereby the tensioning device can be placed in an assemblage of the traction means drive with a drive shaft so as to encompass the drive shaft, with the housing-like part being arranged so as to prevent rotation.
A tensioning device of this type is known form DE 196 31 507 A1. The tensioning mechanism described therein includes a lever and a tensioning wheel, wherein the lever is received in a cup-shaped housing part which also houses a spring element in form of a helical torsion spring. One end of the spring is supported on the housing part which is prevented from rotating when secured in an assemblage that is integrated in the traction means drive, while the other end the spring element acts on a lever, thereby applying a spring force to the lever which can then tighten the traction means guided over the tensioning wheel. The tensioning device described in the above reference is mounted on an assemblage in form of a pump which is driven by the traction means. The traction means run, on one hand, over the tensioning wheel and, on the other hand, over a belt disk. The belt disk is arranged on a drive shaft of the assemblage, with the drive shaft extending through the center of the housing part, and is essentially enclosed by the housing part. This known tensioning device can be used to tighten the traction means on the loose side of the belt which in the aforedescribed embodiment is always located on the same side of the traction means.
Presently, starter generators are developed wherein the traction means are guided, on one hand, over the starter generator and, on the other hand, over the crankshaft of the motor. The starter generator has two functions. Firstly, it allows starting the motor, i.e., it drives the traction means and thereby also the crankshaft via a belt disk. When the motor runs, the starter generator operates as a genuine generator, i.e., it is driven by the driven crankshaft and the traction means. As a result, the location of the loose side of the belt changes depending on the operating mode of the starter generator. With the known tensioning device, however, it is not possible to compensate for this change and to tension the loose side of the belt of the starter generator independent of the operating mode of the starter generator.
The invention is therefore based on the problem to provide a tensioning device which allows tensioning the loose side of the belt depending on the operating mode during torque reversal, for example when used with a starter generator while yet requiring little assembly space at the same time.
FIG. 1 shows a tensioning device 1 according to the invention arranged on a unit 2, for example a starter generator. The tensioning device 1 includes a cylindrical housing-type part 3 comprised of a bottom section 4, a wall section 5 and a cover section 6. The housing-type part 3 has an essentially C-shaped cross-section which is open towards the outside. Two tensioning arms 7, 8 which can rotate against one another are supported separately in the housing-type part 3. For this purpose, each tensioning arm 7, 8 has an annular bearing section 9, 10. The annular bearing sections 9, 10 of the tensioning arms 7, 8 encompass the wall section 5 of the housing-type part 3 that is prevented from rotating with respect to the unit 2. The bearing section 9 is supported by a sliding bearing or radial bearing 11 directly for rotation on the wall section 5. The bearing section 10 of the tensioning arm 8 has a slightly larger diameter and engages with the bearing section 9, as depicted in FIG. 1. The bearing section 10 is supported by a sliding or radial bearing 12 for rotation relative to the bearing section 9.
The tensioning device of the invention advantageously employs two mutually independent tensioning arms that are preferably supported for rotation in the same plane of the housing-like part and have corresponding tensioning rollers that engage with different sections of the traction means. When the torque of the traction means drive is reversed, one of the spring-loaded tensioning arms will always operate on and tighten the currently loose side of the belt. In this way, the traction means will always be sufficiently tightened even if the torque is reversed, allowing the traction means drive to operate reliably. By supporting the tensioning arms in the housing-like part, which also receives the spring element that biases the two tensioning arms, preferably in form of a helical torsion spring, the tensioning device becomes essentially double-acting and can be referred to as a pendulum tensioner. This tensioning device is sufficiently small, so that the tensioning device of the invention can employed even where space is limited, for example in the engine compartment of an internal combustion engine. The tensioning device of the invention can be prefabricated as a separate, complete assembly which needs only to be mounted on the assemblage, for example the starter generator. The drive shaft of the starter generator needs only to be coupled with the belt disk which may be separate from the pre-mounted tensioning device. The tensioning device of the invention does not only have favorable operating characteristics, but is also easy to manufacture and assemble.
The improvement of the present invention can be particularly advantageous for suppliers that supply systems to automobile manufacturers.
According to a particular embodiment of the invention, each tensioning arm can have an annular bearing section which encompasses a cylindrical wall section of the housing-like part. The bearing section of the first tensioning arm is rotationally supported directly on the cylindrical wall section, and the bearing section of the second tensioning arm engages with and is rotationally supported on the wall section of the first tensioning arm. According to this embodiment, the arms are supported by the annular bearing sections that encompass a wall section. The bearing section of the one arm that has a smaller diameter is supported directly on the wall section. The bearing section of the other arm with a slightly larger diameter meshes with the wall section and is directly supported on the other arm. Since the two bearing sections engage with one another, tilting moments can be reduced. The tensioning arms directly contact one another which advantageously minimizes the space requirements in the plane of the belt. The bearing sections are supported by sliding bearings or radial bearings. Advantageously, the spring element, preferably in the form of a helical torsion spring, can be received in an annular space formed between the intermeshing bearing sections.
Frequently, vibrations occur during the operation of the traction means drive, for example when used on the crankshaft of an internal combustion engine, which can be transmitted by the traction means drive to the other components, in this case for example the assemblage on which the tensioning device of the invention is mounted. According to the invention, these oscillations which can be caused, for example, by imbalances of the crankshaft, can be attenuated by placing a friction or damping element, such as a friction disk or a friction coating, between the housing-like part and a tensioning arm. These elements not only dampen the tensioning system against the surroundings, but provide also internal damping. Advantageously, the spring element disposed between the tensioning arms urges the tensioning arms in an axial direction against the friction or damping elements. Hence, the spring element produces the required tensioning force and/or the required to tensioning torque as well as the required axial pre-tensioning force so as to press the tensioning arms against the friction or damping elements and thereby establish the required damping.
According to the invention, the housing-like part includes a bottom section, a wall section and a cover section, and has an essentially C-shaped cross section which is open towards the outside. For installation of the tensioning device, the cover section or the bottom section can be released, allowing insertion of the tensioning arms and the spring element. These components can be secured by known techniques, for example by using a Seeger circlip ring and the like. Means for preventing rotation can also be provided.
As described above, the tensioning device of the invention is mounted on the assemblage which is integrated in the traction means drive. The tensioning device encompasses the drive shaft whose axis is parallel to the axis or axes of the tensioning device. Since the tensioning device is preferably a prefabricated component, which only needs to be mounted on the assemblage, installation can be facilitated by arranging the housing-like part on a flange that has a fastening collar which can be used to secure the tensioning device on the assemblage. The flange has attachment means in form of bores into which attachment screws and the like can be inserted. The flange is constructed to match the attachment features on the assemblage and fitted during installation on the assemblage. In other words, the flange is the only component which has to be specially designed for attaching the tensioning device on the assemblage.
According to another advantageous embodiment of the invention, the bottom section and the wall section can be formed by a flange adapted to secure the tensioning device on the assemblage. With this arrangement, the attachment flange forms simultaneously a portion of the housing-like part. The annular bearing section of the first tensioning arm is therefore supported directly on the flange, and the bottom of the housing is also closed by the flange. In this embodiment of the invention, the bottom section and the wall section need not be separate components.
As described above, the tensioning device of the invention is mounted on an assemblage integrated in the traction means drive, such as the starter generator, wherein the drive shaft of the assemblage extends through the tensioning device which has a central opening. A belt disk about which the traction means are guided, is mounted on the drive shaft. The belt disk can be a separate component which is mounted on a drive shaft after the tensioning device has been installed. Advantageously, a shaft which supports a belt disk or chain disk can be rotatably supported in an opening located on the housing-like part or on a flange supporting the housing-like part. The opening is adapted to receive the drive shaft of the assemblage, wherein the shaft includes connecting means for providing a revolving connection with the drive shaft of the assemblage. With this arrangement of the tensioning device of the invention, the belt or chain disk is arranged for rotation by a shaft in the opening located on the housing-like part or the flange, thereby forming an integral part of the tensioning device of the invention. During the installation of the tensioning device, only the shaft which supports the belt or chain disk has to be connected with the drive shaft of the assemblage to realize the motional coupling. In other words, the so configured tensioning device represents a completely prefabricated component which includes all necessary elements. The connecting means can preferably be formed as a tooth profile, preferably as an inside profile. Alternatively, a spline profile can be employed.
As described above, when the tensioning device is used with a traction means drive with imbalances, the traction means can perform sudden movements which cause the tensioning arm to move rapidly against the spring force. The tensioning arm is hence essentially pushed out of the way by the strike of the traction means. To prevent the tensioning arm from moving too far and thereby losing contact with the traction means for a significant period of time, each tensioning arm can according to the invention have a limit stop which limits movement of the tensioning arm against the spring force. Moreover, the arrangement according to the invention can advantageously also facilitate the installation by providing each tensioning arm with a limit stop which limits the movement caused by the spring force. In other words, these limit stops prevent the tension of the spring element from being released.
According to yet another embodiment of the invention, the tensioning arms which project outwardly from the housing-like part can be constructed and/or formed so that a cup-shaped belt disk or chain disk which can be secured to the drive shaft or integrated for rotation on the tensioning device, at least partially encompasses the side of the housing-like part. According to this embodiment of the invention, the housing-like part is almost entirely received in the cup-like belt or chain disk. As a result, the required space in the plane of the belt can be further minimized, i.e., the plane of the belt can be moved closer to the assemblage.
The invention is not only directed to a tensioning device, but also to an arrangement forming a part of a traction means drive, in particular a belt drive, which includes a tensioning device of the type described above as well as an assemblage formed as a starter generator on which the tensioning device is arranged.
The invention is also directed to the use of a tensioning device of the aforedescribed type in a traction means drive in conjunction with an assemblage in form of a starter generator integrated in the traction means drive.